In conventional manufacturing processes for fibre-reinforced composite parts, fibre material is laid out onto a rigid and inflexible dorn or mandrel. Next, the dorn with the fibre material is placed in a female mould part. The dorn has the function of supporting the fibre material, such as glass fibre material, in the mould part during a casting process in a predefined position and shape. The predefined position and shape of the fibre material onto the dorn is substantially equal to the desired position and shape of a finished fibre-reinforced composite part to be produced.
In particular, sheets of prepreg material may be wrapped around a steel or aluminum mandrel. The fibre-reinforced composite part to be produced is typically batch cured by hanging in an oven. After curing, the mandrel is removed and leaves a hollow fibre-reinforced composite part. Such a process may form strong and robust hollow fibre-reinforced composite tubes, for instance.
If the interior shape of the fibre-reinforced composite part comprises at its edge regions smaller diameters in comparison to other regions of the interior shape, it is difficult to withdraw the dorn after the casting process.
In particular, if producing a large sized blade for wind turbines, a rigid and solid dorn is difficult to withdraw after the cast process. The processed blade comprises only a small opening at its blade root through which the dorn may be removed. Thus, depending on the shape of the rotor blade, the dorn has to comprise a disproportional high amount of flexible material compared to the solid part of the dorn. This is a disadvantage, because the flexible material may inappropriately deform during the casting process, e.g. under the weight of the fibre material laid out onto the surface of the flexible material of the rigid dorn. Moreover, such a dorn with a solid core and a huge amount of flexible material is difficult to handle in particular during storage.